Prior art vehicular exhaust mufflers typically comprise a tubular outer shell defining an oval or circular cross section and a pair of opposed heads mechanically connected to the shell. The shell generally is formed from one or more sheets of metal that are wrapped into the tubular configuration, and are secured in the required shape by a longitudinally extending seam. An inlet and an outlet extend into the opposed heads of the muffler and connect to tubes disposed within the muffler.
The internal configurations of the prior art mufflers have been quite varied and have been determined by both the available space on the vehicle and the particular characteristics of the sound produced by the exhaust gases of a specific engine. The typical prior art muffler includes a circuitous array of tubes extending between and connected to the inlet and the outlet. These respective tubes may communicate with one or more expansion chambers defined by at least one baffle within the muffler. The communication with the expansion tuning chambers typically is provided through the tubes.
In many situations at least one well defined range of noise will persist despite a properly engineered array of tubes and louvers. These residual noise patterns often are attenuated by tuning tubes extending into a closed resonating chamber. The size of the tuning tubes and resonating chambers will be selected in accordance with the frequency of the noise to be attenuated. The resonating chamber of the prior art muffler typically has required at least one additional tube and usually one or more additional baffles to be incorporated into an already complex structure.
The above described typical prior art muffler includes a large number of components that must be assembled in a labor intensive manufacturing process. Specifically, most prior art mufflers require a multilayer outer shell, a pair of heads or end caps, at least two internal tubes and at least two internal baffles. Furthermore, most prior art mufflers will require separate structural elements for expansion chambers, high frequency tuning chambers and/or low frequency resonating chambers. The internal components of the muffler generally are assembled in a very labor intensive process. The various assembled internal components then are inserted into the tubular shell of the muffler which was previously formed from one or more sheets of metal. The opposed muffler heads then are mechanically positioned relative to the shell and are securely mounted thereto.
Attempts have been made to develop stamp formed mufflers in an effort to minimize the number of parts required for the muffler and to reduce the number of manual assembly steps. The logic has been that the stamp forming dies could be configured to define a circuitous route through which the exhaust gases travel. An appropriately circuitous exhaust gas flow pattern could effectively reduce noise.
Several prior art mufflers have merely employed a stamp formed outer shell in combination with a plurality of separate internal members substantially identical to the internal members in the standard muffler having a wrapped outer shell. Examples of mufflers with a stamped outer shell and separate internal baffles and tubes are shown in U.S. Pat. No. 2,943,695 which issued to Jeffords on July 5, 1960, U.S. Pat. No. 3,158,222 which issued to Richmond on Nov. 24, 1964 and U.S. Pat. No. 3,220,508 which issued to Nordquest et al on Nov. 30, 1965.
Other prior art mufflers have employed two stamp formed members configured to define a circuitous air flow pattern without resorting to separate internal tubes and baffles. Examples of such structures are shown in U.S. Pat. No. 2,860,722 which issued to Gerstung on Nov. 18, 1958, U.S. Pat. No. 3,176,791 which issued to Betts et al on Apr. 6, 1965, U.S. Pat. No. 3,638,756 which issued to Thiele on Feb. 1, 1972 and U.S. Pat. No. 4,108,274 which issued to Synder on Aug. 22, 1978. In the above cited U.S. Pat. No. 3,638,756, two opposed stamp formed members were appropriately configured to define not only a circuitous air flow pattern, but also to define low frequency tuning chambers.
Still other prior art mufflers have employed more than two stamp formed members to define an acceptable flow path for exhaust gases through the muffler. For example, U.S. Pat. No. 3,140,755 which issued to Tranel on July 14, 1964, shows two inner stamp formed members configured to define the exhaust gas flow path and two outer stamp formed members configured to define a continuous enclosure around the path defined by the inner members. U.S. Pat. No. 4,396,090 which issued of Wolfhugel on Aug. 2, 1983 shows a muffler wherein the exhaust gas flow passages are formed by stamp forming, while the outer shell is formed from sheet metal wrapped around the stamp formed components.
U.S. Pat. No. 4,456,091 issued to Blanchot on June 26, 1984 and shows a muffler having more than four stamp formed members. More particularly, two internal members are stamp formed to have longitudinally extending corrugations which, when placed in face to face relationship, define a tubular array. Two outer stamp formed members then are configured to define a generally continuous outer enclosure. Separate stamp formed support members are disposed between the outer stamp formed members and the inner stamp formed members to contribute to a proper spaced relationship therebetween. Certain of the corrugated portions of the inner stamp formed members are perforated to provide gas communication between the array of tubes and the enclosure defined by the continuous outer shell. Although this reference relies exclusively on stamp formed members, there are a relatively large number of member that would contribute both to the costs of the product and the assembly time. Similar structures are shown in British Pat. No. 632,013 and British Pat. No. 1,012,463. In both of these British patents, two inner plates are stamp formed to define perforated tubes when mated with one another. Two additional members are stamp formed to define a continuous outer shell which surrounds and is spaced from the perforated tubes. In each of these British patents, either the inner plate members or the outer plate members are formed to define baffles which enable the creation of expansion chambers.
The above described stamp formed mufflers could provide certain cost advantages over conventional mufflers for large production runs. These cost advantages would be attributable to the substantially smaller number of internal components for the muffler, lower labor costs and good material yield. Despite this apparent cost advantage, the prior art stamp formed mufflers have not received significant commercial success, even for the original equipment mufflers which are manufactured in production runs that are large enough to justify the initial tooling costs. One reason for this lack of commerical acceptance has been that the incorporation of resonating chambers into the stamp formed muffler using prior art techniques would require separate components and would add to labor needs, thereby substantially increasing costs of the stamp formed muffler. Low frequency resonating chambers, however, are often required to meet the noise standards of new car manufacturers. Furthermore, the prior art stamp formed mufflers have not provided for both low frequency and high frequency tuning chambers, which often are required to meet selected noise reductions.
In addition to the above described drawbacks, it has been realized that mufflers in general do not account for the fact that exhaust gases cool as they pass through the muffler and therefore acquire different flow and volume characteristics. Furthermore, it has been realized that mufflers in general are not well suited to the specific space availability in or adjacent to the vehicle. Thus, mufflers often are merely added to the bottom of the car thereby adversely affecting both the aesthetics of the vehicle and the air flow profile. Additionally, it has been more costly to manufacture a prior art muffler with more than one inlet and/or more than one outlet or with more than one low frequency resonating chamber because of the additional connections that must be made within the available space.
In view of the above, it is an object of the subject invention to provide an efficient stamp formed muffler.
It is another object of the subject invention to provide a stamp formed muffler with efficient high frequency tuning chambers and/or low frequency resonating chambers.
Another object of the subject invention is to provide a stamp formed muffler having more than one inlet and/or more than one outlet.
A further object of the subject invention is to provide a stamp formed muffler wherein the internal tubes are dimensioned to reflect the temperature and volume changes of the exhaust gases passing therethrough.